We have developed biofilm models of the subgingival plaque on various supports (hydroxyapatite, nitrocellulose membranes, and glass) that are relative simple in concept, but yield reproducible results and mimic the complexity and the diversity of the subgingival microflora. These models appear to be useful for studying the development, maturation, and ultrastructure of the subgingival plaque. The hydroxyapatite model will be used to study the development of the subgingival microflora and the effects that antibiotics exert on the bacteria present. The biofilms grown on the membrane and glass supports will be used to microscopically study the ultrastructure of the biofilms by transmission electron microscopy and confocal laser scanning microscopy. We propose, after refining and validating the model, to use this model to determine the effects of antibiotics on biofilms grown from subgingival plaque collected from sites with periodontitis. These data will be compared to the effect of antibiotics on planktonic cultures of the predominant bacterial isolates present in the biofilm to determine differences in antibiotic susceptibilities in a biofilm relative to planktonic broth cultures. The second objective is to determine the effect of antibiotics, at concentrations obtained therapeutically, on developing biofilms and on a mature biofilms. This will provide a realistic approximation of the effect that antibiotics have on the periodontal flora when used as adjuncts to conventional scaling and root planing. The final specific aim will examine the transfer of antibiotic resistant determinants in the biofilm model. The horizontal transfer of tetQ, a major tetracycline-resistant determinant in the oral flora, will be investigated both within the normal bio-community associated with the subgingival plaque and with exogenous tetracycline-resistant bacteria that are not normal inhabitants of the subgingival community but may occur as transients in this community. We believe the information derived from the experiments described will provide a better understanding of the subgingival flora and the effects that antibiotics may have on this flora.